GPS tracking, are we still lost?

Since the late 1980’s satellite based global position systems (GPS) have provided unique and novel data that has been used to track animal movement. Tracking animals with GPS can provide useful information, but the cost of the technology often limits experimental replication. Limitations on the number of devices available to monitor the behaviour of an animal, in combination with technical constraints, can weaken the statistical power of experiments and create significant experimental design challenges. Wildlife ecologists working in extensive landscapes have pioneered the use of GPS based devices for tracking animals. Wildlife researchers have focused efforts on quantifying and addressing issues associated with technology limitations including spatial accuracy, rate of data collection, battery life and environmental factors causing loss of data. It is therefore not surprising that there have been a significant number of methodological papers published in the literature that have considered technical developments of GPS based animal tracking. Livestock scientists have used GPS data to inform them about behavioural differences in free-grazing experiments. With a shift in focus from the environment to the animal comes the challenge of ensuring independence of the experimental unit. Social facilitation challenges independence of the individual in a group. The use of spatial modeling methods to process GPS data provides an opportunity to determine the degree of independence of data collected from an individual animal within behavioural-based studies. Using location and movement information derived from GPS data researchers have been able to determine the environmental impact of grazing animals. Combining satellite derived remote-sensing data with GPS derived landscape preference indices provides a further opportunity to identify landscape avoidance and selection behaviours. As spatial livestock monitoring tools become more widely used, there will be a greater need to ensure the data and associated processing methods are able to answer a broader range of questions. Experimental design and analytical techniques need to be given more attention if GPS technology is to provide answers to questions associated with free-grazing animals.